The natural pacemaker of the human heart is:

The SA node is located in the:

The delay in conduction of impulse from atria to ventricles occurs at:

The cardiac output is defined as:

During ventricular systole:

The opening of semilunar valves occurs during:

The "lub" sound of the heartbeat is produced due to:

The bundle of His connects:

The average resting heart rate of a normal adult human is approximately:

Purkinje fibers are responsible for: